Titanium bearing material flow control in the manufacture of titanium tetrachloride with silica content monitoring of the titanium product using feedback and feed forward responses

ABSTRACT

This disclosure relates to a process for controlling chlorination reactions in manufacturing titanium tetrachloride in a fluidized bed reactor, followed by processing to form a titanium product comprising an amount of silica, the process comprising: (a) feeding carbonaceous material, titanium bearing material comprising an amount of silica, and chlorine to the fluidized bed reactor to form a gaseous stream, and condensing the gaseous stream to form titanium tetrachloride, a non-condensed gas stream and a condensable product stream; (b) processing the titanium tetrachloride to form a titanium product comprising an amount of silica; (c) analyzing the titanium product comprising an amount of silica to determine the analyzed concentration of silica; (d) identifying a set point concentration of silica; (e) calculating the difference between the analyzed concentration of silica and the set point concentration of silica; (f) measuring the titanium tetrachloride flow to a processing reactor that releases chlorine; (g) measuring the flow of fresh chlorine added to the fluidized bed; (h) measuring the flow of the titanium bearing material added to the fluidized bed reactor and establishing a historic average flow of the titanium bearing material added to the fluidized bed reactor; (i) calculating the chlorine released from the titanium tetrachloride that is processed using the titanium tetrachloride flow data from step (f); (j) calculating the total chlorine flow to the fluidized bed reactor by adding the chlorine flow in step (g) to the chlorine flow calculated in step (i) and establishing a historic average chlorine flow; (k) calculating a unit titanium bearing material consumption per unit chlorine; (l) calculating an estimated current consumption rate of titanium bearing material based on the total chlorine flow from step (j) times the unit titanium bearing material consumption per unit chlorine from step (k); (l) calculating an estimated current consumption rate of titanium bearing material based on the total chlorine flow from step (j) times the unit titanium bearing material consumption per unit chlorine from step (k); and (m) generating a signal based on difference generated in step (e) that provides a feedback response and combining this to the estimated current consumption rate of titanium bearing material from step (l) to provide a feed forward response to control the flow of the titanium bearing material into the fluidized bed reactor.

FIELD OF THE DISCLOSURE

The present disclosure relates to a process for manufacturing titanium products, and in particular to a control process for controlling the flow of titanium bearing material into the fluidized bed reactor and thereby the amount of silicon in the final product.

BACKGROUND OF THE DISCLOSURE

The process for chlorinating titanium containing materials in a fluidized bed reactor is known. Suitable processes are disclosed in the following U.S. Pat. Nos. 2,701,179; 3,883,636; 3,591,333; and 2,446,181. In such processes, particulate coke, particulate titanium bearing materials, chlorine and optionally oxygen or air are fed into a reaction chamber, and a suitable reaction temperature, pressure and flow rates are maintained to sustain the fluidized bed. Gaseous titanium tetrachloride and other metal chlorides are exhausted from the reaction chamber. The gaseous titanium tetrachloride so produced can then be separated from the other metal chlorides and exhaust gas and used to produce titanium dioxide (TiO₂), titanium metal or titanium containing product.

In the chlorination process to prepare titanium tetrachloride, TiCl₄, in a fluidized bed reactor, it is desirable to reduce or control the formation of excess silicon tetrachloride and other undesireable chlorinated organic species. Silicon tetrachloride, SiCl₄, contamination of titanium tetrachloride impacts a variety of quality parameters, such as particle size distribution and primary particle size (indicated by carbon black undertone) of the titanium dioxide produced by oxidation of the TiCl₄. Minimizing or controlling the silica, SiO₂, contamination in the titanium product formed allows for improved performance of the TiO₂ product.

A need exists for a control process that detects the presence of excess, SiO₂, in the untreated oxidized material, and that is capable of correcting the problem.

SUMMARY OF THE DISCLOSURE

In a first aspect, the disclosure provides a process for controlling chlorination reactions in manufacturing titanium tetrachloride in a fluidized bed reactor, followed by processing to form a titanium product comprising an amount of silica, the process comprising:

(a) feeding carbonaceous material, titanium bearing material comprising an amount, typically a minor amount, of silica, and chlorine to the fluidized bed reactor to form a gaseous stream, and condensing the gaseous stream to form titanium tetrachloride, a non-condensed gas stream and a condensable product stream;

(b) processing the titanium tetrachloride to form a titanium product comprising an amount of silica;

(c) analyzing the titanium product comprising an amount of silica to determine the analyzed concentration of silica;

(d) identifying a set point concentration of silica;

(e) calculating the difference between the analyzed concentration of silica and the set point concentration of silica;

(f) measuring the titanium tetrachloride flow to a processing reactor that releases chlorine;

(g) measuring the flow of fresh chlorine added to the fluidized bed;

(h) measuring the flow of the titanium bearing material added to the fluidized bed reactor and establishing a historic average flow of the titanium bearing material added to the fluidized bed reactor ;

(i) calculating the chlorine released from the titanium tetrachloride that is processed using the titanium tetrachloride flow data from step (f);

(j) calculating the total chlorine flow to the fluidized bed reactor by adding the chlorine flow in step (g) to the chlorine flow calculated in step (i) and establishing a historic average chlorine flow;

(k) calculating a unit titanium bearing material consumption per unit chlorine;

(l) calculating an estimated current consumption rate of titanium bearing material based on the total chlorine flow from step (j) times the unit titanium bearing material consumption per unit chlorine from step (k); and

(m) generating a signal based on difference generated in step (e) that provides a feedback response and combining this to the estimated current consumption rate of titanium bearing material from step (l) to provide a feed forward response to control the flow of the titanium bearing material into the fluidized bed reactor.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 sets forth a simplified schematic flow diagram of an embodiment of this disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

Carbonaceous material, titanium bearing material containing some impurities, chlorine, and optionally oxygen or air are fed into a fluidized bed reactor. Typical conditions and specifications for fluidized beds useful for this disclosure are as follows: reaction temperature of about 900° C. to 1300° C., pressure of about 1-3 atmospheres, and a reactor with multiple jets in or near the base. Typically, the point of introduction of the chlorine will be located within about 0 to about 10 feet (about 0 to about 3 m), more typically about 0 to about 8 feet (about 0 to about 2.4 m) and most typically about 0 to about 5 feet (about 0 to about 1.5 m) of the base of the reactor. A most typical location is in the base of the reactor.

The titanium bearing material can be any suitable titanium source material such as titanium containing ores including rutile, ilmenite or anatase ore; beneficiates thereof; titanium containing byproducts or slags; and mixtures thereof. Ordinarily, the titanium bearing material contains iron oxide in the amount of about 0.5-50%, and typically up to about 20% by weight, based on the total weight of the titanium bearing material. This material also typically contains silica. The silica can be present in any form, such as in a silica-containing material or a metallic oxide, but is usually in the form of one or more naturally occurring forms such as sand, quartz, silicates, silica, SiO₂, and Crystobalite. The silica can be in the amount of about 0 to about 25%, and typically about 0.5 to about 1.5%, based on the total weight of the titanium bearing material. The amount of silicon in the titanium bearing material can be determined by XRF analysis or wet chemistry methods or other suitable analytical procedure. The silica can be the source of silicon tetrachloride in the gaseous stream of the fluidized bed reactor.

Suitable carbonaceous material for use in this disclosure is any carbonaceous material which has been subjected to a coking process. Typical is coke or calcined coke which is derived from petroleum or coal or mixtures of such cokes.

As shown in FIG. 1, a titanium bearing material 10 is fed through a control device 13 to the fluidized bed reactor 14. Carbonaceous material 11 is fed directly into the fluidized bed reactor 14. Alternately, carbonaceous material 11 may be fed to the fluidized bed reactor 14 via a control device. The titanium bearing material and the carbonaceous material can also be combined prior to being fed to the fluidized bed reactor 14. The chlorine 12 is fed into the fluidized bed reactor 14 with a recycle stream 27 that recycles chlorine liberated during the oxidation of TiCl₄ to TiO₂ in the oxidation reactor 19 or if chlorine is released during other processing. Gaseous reaction products from the fluidized bed reactor are cooled in condenser(s) 15, in stages, to first condense and remove iron and metal chlorides other than titanium tetrachloride 22. The iron and metal chlorides form the condensable product stream 23. The remaining product from the reactor is then cooled to condense titanium tetrachloride 22 leaving a non-condensed gas stream 21 comprising N₂, COS, SO₂, CO, CO₂, and HCl and other components such as SiCl₄.

The titanium tetrachloride 22 is then processed to form a titanium product 26 comprising an amount, typically a minor amount, of silica. In one specific embodiment, the titanium tetrachloride 22 is then processed in a TiCl₄ processing reactor 19, for example an oxidation reactor, to form a titanium product such as an untreated oxidized material, e.g. titanium dioxide comprising an amount of silica.

A portion or all of the titanium product stream 26, i.e., a sample stream, is sent to an analytical device or analyzer 20 such as a spectrometer, typically an XRF spectrometer, a spectrophotometer and chromatograph.

A sampling system may be required depending on the type of analyzer chosen, the condition of the titanium product and/or the placement of the analyzer. The analytical device can be in-line, meaning installed directly in the path of the stream to be analyzed, typically the titanium product stream 26, or on-line, meaning a portion of the stream to be analyzed, typically the titanium product stream 26, is directed away from the main process stream and toward the analytical device or off-line meaning a sample is collected and analyzed discretely. The sample stream is analyzed for SiO₂ concentration. The analysis is able to proceed quickly, semi continuously and quantitatively. Suitable means of analysis include, but are not limited to, spectroscopy, spectrometry and chromatography. Typically, a spectroscopic method is used to analyze the SiO₂ concentration of the titanium product stream 26. Most typically, XRF spectroscopy is used. Optionally, any portion of the sample stream can be returned to the stream being analyzed, typically the titanium product stream 26.

A first signal 24 (electrical, pneumatic, digital, manual, etc.) is generated from the analysis that is related to the silica, SiO₂, concentration in the titanium product stream 26. The signal proceeds to a control system 17 (such as a distributed control system or other feedback control system) where its value is compared to a set point 18 or determined if it is within a set range. The set point can be a single value reflecting an acceptable SiO₂ concentration or the upper limit of a range of values within which an acceptable SiO₂ concentration can be. This set point 18 is a predetermined or a preset value meaning it is a desired or acceptable SiO₂ concentration. Subtracting the SiO₂ concentration from the analysis from the predetermined acceptable SiO₂ concentration set point can provide the SiO₂ concentration difference that will generate the signal that adjusts the flow of the titanium bearing material 10 to the fluidized bed reactor 14.

Under these conditions the full range of concentration of SiO₂ is about 0 to about 0.3 weight % SiO₂. The set point can be any desired value within this range. Typically, the SiO₂ concentration set range is about 0 to about 0.1 weight % and more typically about 0.01 to about 0.06 weight % of the total content of the titanium product stream 26. It is important that the lower limit to the set range of SiO₂ concentration is not below the detectability limit of the analytical device being used

If the controlled variable does not equal the set point or is outside of the set range, then the difference between the measured controlled variable and set point concentration or concentration range upper limit is determined. A second signal (electrical, pneumatic., digital, etc.) corresponding to this difference is generated either manually or by a suitable feedback controller 17 such as, for example, a proportional, a proportional integral or a proportional integral derivative action controller or other suitable computer software or algorithm that provides a feedback response to the control device 13 which will cause a change in the amount of titanium bearing material being added to the fluidized bed reactor by making a change, typically a proportional change, in the flow rate of the titanium bearing material to the fluidized bed reactor 14. With continuous or discrete monitoring of the controlled variable, the amount of the titanium bearing material added to the fluidized bed reactor can be changed until the controlled variable reaches the set point or is within the set range, as specified for the process. If the SiO₂ concentration in the titanium product stream 26 is determined to be outside of the set range, appropriate changes to the amount of the titanium bearing material being added to the the fluidized bed reactor 14 will be implemented. For example, if it is found that the analyzed SiO₂ concentration is above the set point, the amount of the titanium bearing material being added to the fluidized bed reactor 14 will be increased by an amount proportional to the amount of SiO₂ above the upper limit or set point. Alternately, the amount of titanium bearing material can be decreased if the silicon tetrachloride concentration analyzed is below the set point.

The process further includes measuring the titanium tetrachloride flow to the titanium tetrachloride processing reactor 19, typically an oxidation reactor, using a flow transmitter 28 in the feed line to the reactor. Flow of fresh chlorine added to the fluidized bed reactor is measured using a flow transmitter(s) 29 wherever chlorine is added into the fluidized bed. The flow of the titanium bearing material added to the fluidized bed reactor can be measured using X-ray fluorescence or other suitable analytical technique and any suitable flow measurement technique. A historic average flow of the titanium bearing material is established by averaging the flow of titanium bearing material to the fluidized bed reactor over a suitably long period of time so as to dampen out the impact of minor fluctuations in the process. A suitable time period is a month of fluidized bed operation. The chlorine released from the titanium tetrachloride that is processed, typically oxidized, is calculated using the titanium tetrachloride flow data from step (f) using the molecular weights of titanium tetrachloride and chlorine. The total chlorine flow to the chlorinator is calculated by adding the chlorine flow of the freshly added chlorine to the chlorine released during processing of the titanium tetrachloride that is recycled back to the fluidized bed 14 via recycle gas line 27. A historic average chlorine flow is established by averaging the flow of chlorine to the fluidized bed reactor over a suitably long period of time so as to dampen out the impact of minor fluctuations in the process. A suitable time period is a month of fluidized bed operation.

In step (k), the unit titanium bearing material consumption per unit chlorine can then be calculated. This can be done based on the composition of the titanium bearing material and the known chemistry of the conversion of the titanium bearing material chemical conversion to chlorides or using the following equation: (unit titanium bearing material consumption per unit chlorine)=(historic average flow of the titanium bearing material from step (h))/(historic average chlorine flow from step (j)). This number is dependent on the % titanium dioxide ore being used.

In step (l), the estimated current consumption rate of titanium bearing material is calculated based on the total chlorine flow from step (j) times the unit titanium bearing material consumption per unit chlorine from step (k). A feed forward response is generated by the feed forward controller 30, using the estimated current consumption rate of titanium bearing material from step (l). This is dependent on the size of the plant.

The feed forward response is provided by a feed forward controller selected from the group consisting of a proportional action controller, a proportional integral action controller, a proportional integral derivative action controller; or suitable computer software or algorithm that provides a feed forward response to a control device.

The signals from the feedback and feed forward responses are used control the flow of the titanium bearing material 10 into the fluidized bed reactor 14. In one embodiment, the signal generated in step (l) is added to the estimated current consumption rate of titanium bearing material to control the flow of the titanium bearing material into the fluidized bed reactor. In another embodiment, the signal generated in step (l) is multiplied to the estimated current consumption rate of titanium bearing material to control the flow of the titanium bearing material into the fluidized bed reactor. Alternately, other algorithms can be used.

A typical titanium product produced from the titanium tetrachloride of this disclosure is titanium dioxide in which case the fluidized bed reactor can be followed by oxidation to form a suitable titanium dioxide product such as pigmentary titanium dioxide or titanium dioxide nanoparticles. Other titanium products are also contemplated such as titanium metal which can be made from the titanium tetrachloride by a known processes such as the Kroll and Hunter processes. The process of this disclosure which permits control of the silicon dioxide can produce a useful titanium dioxide product having a low silica concentration.

The disclosure can additionally provide an improved process for controlling chlorination reactions in the manufacture of titanium tetrachloride in a fluidized bed reactor.

To give a clearer understanding of the disclosure, the following example is construed as illustrative and not limitative of the underlying principles of the disclosure in any way whatsoever.

EXAMPLE

SiO₂ concentration in the base pigment is known to correlate with a variety of quality parameters, such as particle size distribution and primary particle size (indicated by carbon black undertone) of the titanium dioxide produced by oxidation of the TiCl₄.

Over a period of approximately three and a half months experimentation was carried out in a plant to demonstrate the effect of automated SiO₂ control. Three hundred and four consecutive product samples were collect and analysed for SiO₂. This was compared with 304 samples prior to any silica control. The variability in the product SiO₂ concentration was measured and provided in Table 1.

TABLE 1 Base TiO₂ Product SiO₂ Concentration Standard Deviation TiO₂ Bearing Material Feed Control Method 0.0489 SiO₂ Based TiO₂ Bearing Material Feed 0.0224 Control Method Reduction in Base Pigment SiO₂ Standard 54% Deviation The previous TiO2 bearing material feed control method noted in Table 1 was based on reactions in the chlorinator including theoretical consumption rate of titanium bearing materials and inferential chlorine discharge rate. From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of the disclosure, and without departing from the spirit and scope thereof, can make various changes and modification of the disclosure to adapt it to various usages and conditions.

Having thus described and exemplified the disclosure with a certain degree of particularity, it should be appreciated that the following claims are not to be limited but are to be afforded a scope commensurate with the wording of each element of the cairns and equivalents thereof. 

What is claimed is:
 1. A process for controlling chlorination reactions in manufacturing titanium tetrachloride in a fluidized bed reactor, followed by processing to form a titanium product comprising an amount of silica, the process comprising: (a) feeding carbonaceous material, titanium bearing material comprising an amount of silica, and chlorine to the fluidized bed reactor to form a gaseous stream, and condensing the gaseous stream to form titanium tetrachloride, a non-condensed gas stream and a condensable product stream; (b) processing the titanium tetrachloride to form a titanium product comprising an amount of silica; (c) analyzing the titanium product comprising an amount of silica to determine the analyzed concentration of silica; (d) identifying a set point concentration of silica; (e) calculating the difference between the analyzed concentration of silica and the set point concentration of silica; (f) measuring the titanium tetrachloride flow to a processing reactor that releases chlorine; (g) measuring the flow of fresh chlorine added to the fluidized bed; (h) measuring the flow of the titanium bearing material added to the fluidized bed reactor and establishing a historic average flow of the titanium bearing material added to the fluidized bed reactor; (i) calculating the chlorine released from the titanium tetrachloride that is processed using the titanium tetrachloride flow data from step (f); (j) calculating the total chlorine flow to the fluidized bed reactor by adding the chlorine flow in step (g) to the chlorine flow calculated in step (i) and establishing a historic average chlorine flow; (k) calculating a unit titanium bearing material consumption per unit chlorine; (l) calculating an estimated current consumption rate of titanium bearing material based on the total chlorine flow from step (j) times the unit titanium bearing material consumption per unit chlorine from step (k); and (m) generating a signal based on difference generated in step (e) that provides a feedback response and combining this to the estimated current consumption rate of titanium bearing material from step (l) to provide a feed forward response to control the flow of the titanium bearing material into the fluidized bed reactor.
 2. The process of claim 1 wherein the analyzed concentration of silica is greater than the set point concentration of silica.
 3. The process of claim 1 wherein the analyzed concentration of silica is less than the set point concentration of silica.
 4. The process of claim 2 wherein the analyzed concentration of silica is greater than the set point concentration of silica and the feedback response comprises increasing the amount of titanium bearing material being introduced into the fluidized bed reactor.
 5. The process of claim 3 wherein the analyzed concentration of silica is less than the set point concentration of silica and the feedback response comprises decreasing the amount of titanium bearing material being introduced into the fluidized bed reactor.
 6. The process of claim 1 wherein the analyzed concentration of silica is determined by analyzing the titanium product.
 7. The process of claim 1 wherein analyzing the titanium product is achieved by spectroscopy, spectrometry or chromatography.
 8. The process of claim 7 wherein analyzing the titanium product is by XRF spectroscopy.
 9. The process of claim 1 wherein the silica is present in the titanium product in the amount of about 0 to about 0.3 weight %, based on the total weight of the titanium product.
 10. The process of claim 1 wherein the silica is present in the titanium product in the amount of about 0.0 to about 0.1 weight % based on the total weight of the titanium product.
 11. The process of claim 1 wherein the silica is present in the titanium product in the amount of about 0.01 to about 0.06 weight %, based on the total weight of the titanium product.
 12. The process of claim 1 wherein the desired concentration of silica is about 0.01 to about 0.3 mole %.
 13. The process of claim 1 wherein the signal is electrical, pneumatic, digital or manual.
 14. The process of claim 1 wherein the feedback response is provided by a feedback controller selected from the group consisting of a proportional action controller, proportion integral action controller, a proportional integral derivative action controller; or suitable computer software or algorithm that provides a feedback response to a control device.
 15. The process of claim 1 wherein the processing reactor is an oxidation reactor and the titanium tetrachloride is oxidized to a titanium product comprising titanium dioxide.
 16. The process of claim 1 wherein the feed forward response is provided by a feed forward controller selected from the group consisting of a proportional action controller, a proportional integral action controller, a proportional integral derivative action controller; or suitable computer software or algorithm that provides a feed forward response to a control device.
 17. The process of claim 1 wherein the unit titanium bearing material consumption per unit chlorine is calculated using the following equation: (unit titanium bearing material consumption per unit chlorine)=(historic average flow of the titanium bearing material from step (h))/(historic average chlorine flow from step (j)). 